23. Year 1700 (Charles Townshend popularizes) Growing the same crop repeatedly on the same land eventually depletes the soil of different nutrients. Farmers avoided a decrease in soil fertility by practicing crop rotation. Different plant crops were planted in a regular sequence so that the leaching of the soil by a crop of one kind of nutrient was followed by a plant crop that returned that nutrient to the soil. Crop rotation was practiced in ancient Roman, African, and Asian cultures. During the Middle Ages in Europe, a three-year crop rotation was practiced by farmers rotating rye or winter wheat in year one, followed by spring oats or barley in the second year, and followed by a third year of no crops. In the 18th century, British agriculturalist Charles Townshend aided the European agricultural revolution by popularizing a four- year crop rotation with rotations of wheat, barley, turnips, and clover. In the United States, George Washington Carver brought his science of crop rotation to the farmers and saved the farming resources of the south. 24. 14/3/1794 (Cotton gin is invented) A Cotton Gin (short for cotton engine) is a machine that quickly and easily separates the cotton fibers from the seedpods and the sometimes sticky seeds, a job previously done by slave workers. These seeds were either used again to grow more cotton or if badly damaged were disposed of. It uses a combination of a wire screen and small wire hooks to pull the cotton through the screen, while brushes continuously remove the loose cotton lint to prevent jams. The term "gin" is an abbreviation for engine, and means "device". According to Joseph Needham a precursor to the cotton gin was present in India, which was known as a charkhi, which had two elongated worms that turned its rollers in opposite directions. The modern cotton gin was later created by the American inventor Eli Whitney in 1793 to mechanize the production of cotton fiber. The invention was granted a patent on March 14, 1794. The cotton gin was credited for increasing assets in the American economy.